Y-junction strip line switchable circulator contained within a hollow low magnetic permeability cylindrical tube



Dec. 27, 1966 K. L. CARR 3,295,074

Y-JUNCTION STRIP LINE SWITCHABLE CIRCULATOR CONTAINED WITHIN A HOLLOW LOW MAGNETIC PERMEABILITY CYLINDRICAL TUBE 5 Sheets-Sheet 1 Filed March 5, 1965 PRIOR ART INVENTOR.

KENNETH L. CARR BY WM 3% ATTORNEYS Dec. 27, 1966 K. L. CARR 3,295,974

Y-JUNCTION STRIP LINE SWITCHABLE CIRCULATOR CONTAINED WITHIN A HOLLOW LOW MAGNETIC PERMEABILITY CYLINDRICAL TUBE Filed March 5, 1965 5 Sheets-Sheet 3 AAAAA INTI gr n

INVENTOR.

KENNETH L. CARR ATTORNEYS United States Patent Y-JUNCTION STRIP LINE SWITCHABLE CIRCU- LATOR CONTAINED WITHIN A HOLLOW LOW MI1J&%NETIC PERMEABILITY CYLINDRICAL T B Kenneth L. Carr, Bedford, Mass, assiguor to Ferrotec, Iuc., Newton, Mass, a corporation of Massachusetts Filed Mar. 5, 1965, Ser. No. 437,425 g Claims. (Cl. 3331.1)

This invention relates in general to non-reciprocal ferrite devices for controlling the transmission of electromagnetic waves and more particularly pertains to a symmetrical Y-junction switchable circulator utilizing strip transmission line.

A circulator is a structure, haivng three or more arms, which is characterized by allowing wave energy applied at any one arm to be transmitted to only one of the other arms, the direction of transmission between arms always being in the same sense so that the device is non-reciprocal. That is, in a circulator having three arms, wave energy applied at the first arm is almost entirely transmitted to the second arm, wave energy applied at the second arm is almost entirely transmitted to the third arm, and wave energy applied at the third arm is almost entirely transmitted to the first arm.

Symmetrical Y-junction circulators are widely used in controlling the transmission of UHF and SHF waves. At the longer wavelengths, the symmetrical Y circulator utilizes strip transmission line, whereas waveguide is generally preferred for the shorter wavelengths. In the conventional strip line circulator the center conductor of the strip line is a spider having three arms in a symmetrical configuration. The spider is sandwiched between a pair of ferrimagnetic discs with the arms extending outside the sandwich and this assemblage is disposed between a pair of ground plane plates. In the operation of the circulator, the ferrimagnetic members are within a magnetic field established by an electromagnet having its pole pieces mounted upon the ground plane plates. In order to conserve power without decreasing the intensity of the magnetic field, the pole pieces are brought as close together as the ground plane plates permit. To obtain close spacing and to aid in positioning the pole pieces, the ground plane plates are provided with recesses which accommodate the pole pieces. In the conventional strip line Y- junction circulator, the spacing between the ground planes is uniform and is usually so small as to preclude placing an electromagnetic coil around the ferrimagnetic members. Further in the conventional strip line Y-circulator, the ferrimagnetic discs are disposed within broad rings of dielectric material which correct the impedance mismatch caused in the strip line by the ferrimagnetic discs. The broad rings prevent an electromagnetic coil from closely encircling the ferrimagnetic discs even if the coil could be interposed between the ground plane plates.

The invention is an improvement upon the conventional strip line Y-junction switchable circulator and resides in a structural arrangement which permits an electromagnetic coil to closely encircle the ferrirnagnetic discs. This placement of the electromagnetic coil insures excellent coupling of the magnetic field to the ferrimagnets and conduces to efiicient use of the power applied to the coil.

The invention, both as to its construction and manner of operation, can be apprehended from the following exposition which is intended for study conjunctively with the accompanying drawings in which:

FIG. 1 is a partially exploded perspective view of a prior art symmetrical Y-junction strip line circulator;

FIG. 2 illustrates a conventional air filled strip transmission line;

Patented Dec. 27, 1966 FIG. 3 depicts a strip transmission line having a constant characteristic impedance despite the presence in the line of two unlike dielectric mediums;

FIG. 4 is a perspective view of an embodiment of the invention that is partially exploded to display its internal construction;

FIG. 5 depicts a top plan view of the invention; and

FIG. 6 shows a cross-section of the invention taken along the parting plane 6-6 of FIG. 5.

A prior art strip line symmetrical Y-junction switchable circulator of conventional construction is depicted in FIG. 1. The center conductor of the strip line is a spider 1, the spider having three symmetrical arms and being sandwiched between two ferrite discs 2 and 3 so that the arms protrude. The ferrite discs, in turn, are disposed between ground plane plates 4 and 5 which are uniformly spaced apart. The discs are fitted within broad dielectric rings 6 and 7 which match the characteristic impedance of the ferrite filled segment of the strip line to the characteristic impedance of the air filled segment. Each ground plane plate has a recess, such as recess 8, which receives the pole of a C-shaped core 9 of an electromagnet having a coil 10. When assembled and in operation, the energized coil causes the electromagnet to establish a magnet field of such intensity as to bias the ferrimagnetic discs below resonance. An alternative man ner of operation requires the ferrimagnetic discs to be biased above resonance. As a more intense magnetic field is required for above resonance biasing, the more usual method is to use a less intense field so as to operate below resonance. The three arms of the strip line center conductor are joined to the center conductors of coaxial connectors 11, 12, and 13. The ground plane plates 4 and 5 are held in spaced apart relation by coupling plates 14, 15, and 16, and the coaxial connectors protrude through the coupling plates. In the strip line portion of the conventional Y-junction circulator, wave propagation occurs in three ditferent mediums, viz.,.in air, in the dielectric rings, and in the ferrite discs. As the characteristic impedance of the air filled portion of the strip line differs from the characteristic impedance of the ferrite filled portion of the strip line, dielectric rings 6 and 7 are employed in an effort to correct the impedance mismatch.

The characteristic impedance of a strip transmission line is given, approximately, by the equation where Z is the characteristic impedance e is the dielectric constant of the wave transmission medium 12 is the spacing between ground planes, and

w is the width of the center conductor.

The equation assumes the thickness of the center conductor to be negligible; that is, that the thickness of the center conductor is considered to be vanishingly small. From the equation it can be deduced that a change in characteristic impedance caused by an increase in the dielectric constant 2 can be offset by increasing the spacing b between ground planes.

FIG. 2 shows a conventional air filled strip transmission line in which e the dielectric constant of air is taken to be equal to unity, the center conductor is a thin strip having a width w, and the ground plane plates are separated by the distance 17.

Where a segment of the strip line of FIG. 2 is filled with ferrimagnetic blocks 17 and 18, as depicted in FIG. 3, the characteristics impedance of the line can be maintained unchanged by increasing the spacing between ground planes for the length of the segment to offset the higher dielectric constant e of the ferrites.

In the embodiment of the invention depicted in FIGS. 4, 5, and 6, dielectric matching rings are not used. To maintain an impedance match, that embodiment utilizes an increase in the spacing between ground planes. In addition to maintaining a matched impedance, the increased ground plane spacing permits an electromagnetic coil to be placed so as to closely envelope the ferrimagnetic discs.

The ground planes of the strip line circulator depicted in FIGS. 4, 5, and 6 are constituted by metallic discs 20 and 21, and the center conductor of the strip line is a thin flat member 22 having three arms meeting in a symmetrical junction. A pair of ferrimagnetic discs 23 and 24 fill the space between the ground plane discs and the center conductor, except for the tapered ends of the three arms which protrude beyond the ferrite members. The tapered end of each arm is joined to the center conductor of a coaxial connector.

The entire strip line is contained within a hollow cylindrical tube formed by bobbins 26 and 27. 'Each bobbin has many turns of wire wound upon it so as to form an electromagnet. The windings 28 and 29 on the bobbins, are, in the assembled device, connected together so that their magnetic fields aid each other; that is, the windings are connected so that they, in effect, operate as a single electromagnet which establishes an intense magnetic field.

As best shown in FIG. 4, each bobbin has a flange in which three semicircular grooves are provided. When the bobbins are assembled with their flanges in contact, as in FIG. 6, the grooves form three circular holes through which extend the center conductors of three coaxial connectors 30, 31, and 32. The coaxial connectors are integral parts of three spacers 33, 34, and 35. The spacers are, preferably, arcuates plates that fit closely against the periphery of the bobbin flanges. As best shown in FIG. 6, the center conductor 25 of coaxial con nector 30 is reduced in diameter where it enters the circular hole in the flanges of the bobbins. This is done to maintain an unvarying characteristic impedance throughout the coaxial line.

The characteristic impedance of a coaxial line is given approximately by the equation p g d where Z is the characteristic impedance e is the dielectric constant of the medium in the line D is the internal diameter of the outer conductor, and d is the diameter of the inner conductor.

Where the medium in the line has a fixed dielectric constant and the internal diameter D of the outer conductor changes, the characteristic impedance can be maintained at a fixed value by altering d, the diameter of the inner conductor, to compensate for changes in D.

It can be seen from the cross-sectional view of FIG. 6 that where the diameter of the outer conductor of the coaxial line changes, the diameter of the inner conductor 25 is altered to maintain a constant characteristic impedance for the coaxial line.

Secured to spacers 33, 34, and 35 are circular plates 36 and 37. The plates are provided with bosses that fit into the central openings of the bobbins so that they are close to the ferrite discs 23 and 24. Where fast switching is desired, the pole pieces 36 and 37 are, preferably, made of a ferrite material; where slower switching is tolerable, plates 36 and 37 can be made of soft iron or some other material offering low magnetic reluctance. To further conduce to a low reluctance magnetic path for the field established by the electromagnetic coils, the magnetic core 38, depicted in FIG. 4, is arranged so that its poles rest upon plates 36 and 37. In lieu of the illustrated magnetic core 38, a magnetically permeable clamshell structure may be employed which encases the circulator except where openings are provided for the coaxial connectors.

In order to have the electromagnetic coils closely encircle the ferrite discs, the wall of the cylinder formed by the bob-bins preferably is very thin. The cylinder, formed by the bobbins, is constructed from a material exhibiting low magnetic permeability so as not to provide an easy path for the magnetic flux of the field established by current flow in the electromagnet. That is, the objective is to cause the magnetic field to be concentrated between the ground plane plates 20 and 21 so that the ferrimagnets 23 and 24 are situated in the most intense portion of the magnetic field. It is, therefore, highly desirable to prevent the wall of the cylinder from offering an easy path for magnetic flux as such a path would detract from the intensity of the magnetic field applied to the ferrimagnets. Types of stainless steels are available which are characterized by high mechanical strength, lo-w magnetic permeability, and good electrical conductivity. Such stainless steels are suited for serving in the bobbins as their high mechanical strength permits the cylinder wall to be very thin and their high magnetic reluctance is of advantage in enhancing the switching time of the circulator.

To switch the circulator, it is necessary only to reverse the direction of the current flowing in the electromagnet. The reversal of current flow, in turn, reverses the direction of the magnet field applied to the ferrimagnets 23 and 24 and causes the circulator to transmit wave energy in the counter direction. That is, when the magnetic field across ground plates 20 and 21 is in one direction, the circulator transmits wave energy only in the clockwise direction as viewed in FIG. 5; when the magnetic field across the ground plates is reversed in direction, the circulator then transmits wave energy only in the counterclockwise direction as viewed in FIG. 5. For example, a signal impressed on coaxial connector 30 is transmitted to connector 31 when the magnetic field is in one direction and when the direction of the magnetic field is reversed, the signal is switched to connector 32.

While the electromagnet, in the described embodiment, is wound upon two bobbins, it is obvious that the cylinder formed by the bobbins could be a unitary structure upon which the coil is wound. Further, the cylinder can be fabricated of a non-metallic, non-magnetic'subst-ance having high mechanical strength. If such a substance is a poor electrical conductor, good electrical conductivity can be obtained by plating it with a conductive metal or by otherwise treating it. Other changes which do not depart from the teaching of the invention can be made and indeed are apparent to those skilled in the art. For example, the ground planes, which have been depicted as metallic discs 20 and 21, may simply be conductive foils plated upon the pole pieces 36 and 37.

As changes can be made in the illustrated embodiment that do not alter the essential nature of the invention, it is intended that the scope of the invention be delimited by the appended claims and include such structures as do not in essence depart from the defined domain.

What is claimed is:

1. A circulator comprising:

(1) a hollow tube of low magnetic permeability;

(2) means in the tube constituting the ground planes of a strip transmission line;

(3) 'a member constituting the center conductor of the strip transmission line, the center conductor having a plurality of arms symmetrical about and extending from a central portion;

(4) a ferrimagnetic medium filling the space between the center conductor and the ground planes;

(5) an electromagnetic coil closely surrounding the tube and encircling the ferrimagnetically filled strip t ansm ssion line;

(6) means for concentrating across the ground planes in the tube the magnetic field established by an electrical current flowing in the electromagnetic coil;

(7) and means external of the tube providing electrical coupling to the center conductor of the strip transmission line.

2. A circulator comprising:

(1) a hollow cylinder having a thin wall of low magnetic permeability;

(2) a pair of spaced, electrically conductive, circular plates disposed within the cylinder, the plates being the ground planes of a strip transmission line;

(3) a member constituting the center conductor of the strip transmission line, the center conductor having a plurality of symmetrically arranged arms extending from a central portion;

(4) a pair of fern'magnetic discs in the cylinder filling the space between the center conductor and the ground planes;

(5) an electromagnetic coil closely surrounding the cylinder in the vicinity of the ferrimagnetic discs;

(6) means for concentrating across the ground plane plates the magnetic field established by the electromagnetic coil;

(7) and means external of the cylinder providing electrical coupling to the arms of the strip transmission lines center conductor.

3. A switchable Y-circulator comprising:

(1) a hollow, electrically conductive cylinder having a thin wall of low magnetic permeability;

(2) a pair of spaced, conductive, circular plates disposed within the cylinder, the plates being the ground planes of a strip transmission line;

(3) a member constituting the center conductor of the strip transmission line, the center conductor having three symmetrically arranged arms extending from a central portion;

(4) a pair of ferrimagnetic discs filling the space between the center conductor and the ground planes;

(5) an electromagnetic coil closely surrounding the tube and encircling the ferrimagnetically filled strip transmission line;

(6) pole pieces disposed in the ends of the hollow cylinder, the pole pieces being contiguous to the ground plane plates;

(7) and means external of the cylinder providing electrical coupling to the arms of the strip transmission lines center conductor.

4. A switchable Y-circulator comprising:

(1) a pair of bobbins forming a hollow cylinder whose wall is of low magnetic permeability;

(2) each bobbin having an electromagnetic coil wound about its exterior;

(3) a pair of spaced, electrically conductive circular plates disposed within the cylinder, the conductive plates constituting the ground planes of a strip transmission line;

(4) a member constituting the center conductor of the strip transmission line, the center conductor having three symmetrically arranged arms extending from a central portion;

(5) a pair of ferrimagnetic discs in the cylinder, the discs being on opposite sides of the center conductor and filling the space between the center conductor and the ground planes whereby wave propagation in the strip line occurs principally in the ferrimagnetic medium;

(6) means for concentrating across the ground plane plates the magnetic field established by the electromagnetic coils, said means including pole pieces having portions disposed in the ends of the hollow cylinder contiguous to the ground plane plates;

(7) and means external of the cylinder providing electrical coupling to the arms of the strip transmission lines center conductor.

5. A circulator comprising:

(1) a hollow, electrically conductive tube of low magnetic permeability;

(2) means in the tube constituting the ground planes. of a strip transmission line, the ground planes being electrically connected to the conductive tube;

(3) a member disposed in the tube and constituting the center conductor of the strip transmission line, the center conductor having a plurality of symmetrically arranged arms extending from a central portion;

(4) a pair of ferrimagnetic members situated within the tube, the ferrimagnetic members being interposed in the space between the center conductor and the ground planes;

(5) an electromagnetic coil closely surrounding the tube in the vicinity of the ferrimagnetic members; (6) means for concentrating across the ground plane plates the magnetic field established by the electromagnetic coil;

(7) and means extending through apertures in the wall of the tube for providing electrical coupling to the arms of the center conductor.

References Cited by the Examiner UNITED STATES PATENTS 3,185,941 5/1965 Freiberg 333-1.1

HERMAN KARL SAALBACH, Primary Examiner, P, L. G E NSLER, Assistant Examiner, 

1. A CIRCULATOR COMPRISING: (1) A HOLLOW TUBE OF LOW MAGNETIC PERMEABILITY; (2) MEANS IN THE TUBE CONSTITUTING THE GROUND PLANES OF A STRIP TRANSMISSION LINE; (3) A MEMBER CONSTITUTING THE CENTER CONDUCTOR OF THE STRIP TRANSMISSION LINE, THE CENTER CONDUCTOR HAVING A PLURALITY OF ARMS SYMMETRICAL ABOUT AND EXTENDING FROM A CENTRAL PORTION; (4) A FERRIMAGNETIC MEDIUM FILLING THE SPACE BETWEEN THE CENTER CONDUCTOR AND THE GROUND PLANES; (5) AN ELECTROMAGNETIC COIL CLOSELY SURROUNDING THE TUBE AND ENCIRCLING THE FERRMAGNETICALLY FILLED STRIP TRANSMISSION LINE; (6) MEANS FOR CONCENTRATING ACROSS THE GROUND PLANES IN THE TUBE THE MAGNETIC FIELD ESTABLISHED BY AN ELECTRICAL CURRENT FLOWING IN THE ELECTROMAGNETIC COIL; (7) AND MEANS EXTERNAL OF THE TUBE PROVIDING ELECTRICAL COUPLING TO THE CENTER CONDUCTOR OF THE STRIP TRANSMISSION LINE. 